What is the minimum height above the trap for a standpipe, such as that used for a clothes washer?

The correct minimum height above the trap for a standpipe, particularly in the context of a clothes washer, is established at 18 inches. This elevation is crucial for ensuring proper drainage and preventing any potential siphoning of wastewater back into the appliance. The height is designed to create sufficient air space above the trap, which helps maintain the necessary water seal that prevents sewer gases from entering the living space.

Setting the standpipe at this height also addresses concerns related to overflows and flooding, as it minimizes the risk of water backing up into the appliance. Additionally, proper installation must comply with plumbing codes that dictate these requirements to ensure safety and efficiency in the plumbing system.